Why pay a lot for a compact fluorescent lightbulb when you can buy a "regular" incandescent lightbulb for less? Because the real cost of light is not the cost of the bulb, but the electricity that the lightbulb uses. Compact fluorescents are available that give about the equivalent light of a 100-watt incandescent, yet consume only 25 to 30 watts.

In the past, we've tested the "life" of compact fluorescents--that is, how long they last. For a past test, we focused on what it's like to live with a compact fluorescent, and whether or not they're getting closer to the light of an incandescent.

The industry has standard procedures for lightbulb testing. While these tests are accurate, they also leave out some key aspects of how a person actually uses a lightbulb. The most important is the "first use," or what happens when the bulb is first taken out of the package. Also important to consider is how long it takes for the bulb to "warm up" to full power. Incandescents are practically instantaneous. Our tests seek to determine, among other things, if compact fluorescents behave the same way.

For our panel test, each of the 30 participants first performs a reading task in a room illuminated only by one table lamp. In the lamp, there is either a 100-watt incandescent, our "best" compact fluorescent, or our "worst" compact fluorescent. After the reading task, each panelist proceeds to another room, where six compact fluorescents and one incandescent are displayed (below, right). Panelists make comparative judgments of the different lightbulbs.